Plasma processing is commonly used for many semiconductor fabrication processes for manufacturing integrated circuits, flat-panel displays, magnetic media, and other devices. A plasma, or ionized gas, is generated inside a processing chamber by application of an electromagnetic field to a low-pressure gas in the chamber, and then applied to a workpiece to accomplish a process such as deposition, etching, or implantation. The plasma may also be generated outside the chamber and then directed into the chamber under pressure to increase the ratio of radicals to ions in the plasma for processes needing such treatments.
Plasma may be generated by electric fields, by magnetic fields, or by electromagnetic fields. Plasma generated by an electric field normally uses spaced-apart electrodes to generate the electric field in the space occupied by the gas. The electric field ionizes the gas, and the resulting ions and electrons move toward one electrode or the other under the influence of the electric field. The electric field can impart very high energies to ions impinging on the workpiece, which can sputter material from the workpiece, damaging the workpiece and creating potentially contaminating particles in the chamber. Additionally, the high potentials accompanying such plasmas may create unwanted electrical discharges and parasitic currents.
Inductively coupled plasmas are used in many circumstances to avoid some effects of capacitively coupled plasmas. An inductive coil is disposed adjacent to a plasma generating region of a processing chamber. The inductive coil projects a magnetic field into the chamber to ionize a gas inside the chamber. The inductive coil is frequently located outside the chamber, projecting the magnetic field into the chamber through a dielectric window. The inductive coil is frequently driven by high-frequency electromagnetic energy, which suffers power losses that rise faster than the voltage applied to the inductive coil. Thus, strong coupling of the plasma source with the plasma inside the chamber decreases power losses. Control of plasma uniformity is also improved by strong coupling between the plasma source and the plasma.
As device geometry in the various semiconductor industries continues to decline, process uniformity in general and plasma uniformity in particular, becomes increasingly helpful for reliable manufacture of devices. Thus, there is a continuing need for inductive plasma processing apparatus and methods.